dsa: mv88e6xxx: 6161: Use chip wide MAX MTU

The datasheets suggests the 6161 uses a per port setting for jumbo
frames. Testing has however shown this is not correct, it uses the old
style chip wide MTU control. Change the ops in the 6161 structure to
reflect this.

Fixes: 1baf0fac ("net: dsa: mv88e6xxx: Use chip-wide max frame size for MTU")
Reported by: 曹煜 <cao88yu@gmail.com>
Signed-off-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>